test: add test for issue 15895

It was fixed earlier in the Go 1.8 cycle.
Add a test.

Fixes #15895

Change-Id: I5834831235d99b9fcf21b435932cdd7ac6dc2c6e
Reviewed-on: https://go-review.googlesource.com/28476
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue15895.go

+// compile
+
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// func bad used to fail to compile.
+
+package p
+
+type A [1]int
+
+func bad(x A) {
+	switch x {
+	case A([1]int{1}):
+	case A([1]int{1}):
+	}
+}
+
+func good(x A) {
+	y := A([1]int{1})
+	z := A([1]int{1})
+	switch x {
+	case y:
+	case z:
+	}
+}